1. Field of the Invention
The invention relates to a zoom lens structure. In particular, the zoom lens has a structure to permit a high zoom capability.
2. Description of Related Art
A finite optical system is used widely in various electronic image devices, which require focusing and shooting by an optical system. In particular, a finite optical system is used for a lens system in digital still cameras, close-up shooting optical systems, enlargement development optical systems, reduction development optical systems, projection lenses for video projectors using liquid-crystal display and the like.
Among known finite optical systems, a finite single focus lens has limited use. Accordingly, a special optical system is required for each purpose. On the other hand, a finite zoom lens has a wider range of uses compared to a single focus lens. However, a finite zoom lens lacks a variety of lenses. A finite zoom lens is used widely in lens systems for 35 mm still cameras, lens systems for 16 mm cinema scope cameras, and lens systems for televisions. A shooting zoom lens with low magnification, around 1/50.times..about.1/30.times., with wide field angle, is advantageous for a compact and high image quality image input optical system in electronic image equipment.
A low magnification and wide field angle zoom lens is disclosed in Japanese Laid-Open Patent Publication No. 3-71686 (JP 686). However, a zoom method of the zoom lens in JP 686 encounters problems in shifting to a high magnification, and a zoom locus for each lens group is complicated. Moreover, with the zoom lens of JP 686, an optical system for a measurement projection equipment requires strong telecentricity. Additionally, an effective F-number is relatively large at around F/3.5-F/6.5. Therefore, the zoom lens is not sufficient to shoot an object with a dark and/or black design, depending on illumination conditions. Thus, a bright, wide angle high zooming capability and performance optical system has been long desired.
For an optical system in electronic image equipment, the system must cope with numerous uses. Therefore, a special optical system is needed to correspond to each purpose. In other words, in a conventional zoom lens, a special optical system is required for each purpose, making this optical system very inefficient and uneconomical.
With an optical system for use in photo-imaging systems with high resolution, a zoom lens should favorably correct chromatic aberrations of magnification. Further, the zoom lens should be bright, have high performance, be capable of shifting to high zooming, have a short conjugal length, be capable of presenting wide field angle, and have small distortion and fluctuation during zooming. Additionally, the zoom lens should be capable of securing sufficient amount of light in a marginal zone, to minimize shading.
Considering the problems described above, embodiments of the present invention aim to provide a high performance, high zooming ratio zoom lens capable of coping with a wide variety of utilization purposes.